This is a proposal to pursue epidemiologic studies in Chile, on the association between nitrate exposure and stomach mortality and, within a broader context, to test the hypothesis that N-nitroso compounds may be carcinogenic for man. The initial study, already published, demonstrated a correlation between nitrate exposure and stomach cancer mortality in Chile. The proposed study is designed to meet three major objectives: 1) To determine whether a significant difference in exposure to variables indicative of a high nitrate intake exists in Chile between two groups of stomach cancer patients and their ill and well controls; 2) To explore for additional factors which might be of significance, other than cumulative nitrate exposure demonstrated in our previous correlation study; 3) To determine whether a correlation exists between nitrate/nitrite exposure indicators and stomach cancer in low and high risk areas of Chile. In order to meet all three objectives, a case-control and a nitrate ecology study are proposed, to be carried out concurrently during a 20-month period. In the case-control study, cases, hospital and neighborhood controls will be interviewed. A questionnaire specially designed to record long-term data has been already pilot-tested. The analysis of combinations of ten variables throughout life periods defined by residence landmarks will explore differences in patterns between cases and controls. The nitrate ecology study includes the collection of specimens to determine nitrate/nitrite contents in urine and saliva of school children and in food specimens, both in high and low risk areas. Confirmation of the correlation study by these proposed studies will help to substantiate the role of N-nitroso compounds in man. Therefore, the implications for the United States will be highly significant.